Semiconductor capacitors including a semiconductor substrate are used for on-vehicle devices, industrial devices, and the like as capacitors excellent in both voltage endurance and heat resistance.
One such semiconductor capacitor is disclosed in Japanese Patent Application Laid-Open No. 2006-261416. FIG. 5 shows a semiconductor capacitor 1000 disclosed in the foregoing application. As shown therein, the semiconductor capacitor 1000 includes a semiconductor substrate 101, formed, for example, of Si (silicon). A plurality of trenches 102 are formed on a first principal surface (the upper principal surface as viewed in FIG. 5) of the semiconductor substrate 101.
A dielectric film (insulating film) 103 is formed on an inner wall of each of the trenches 102. The dielectric film 103 is formed of, for example, an oxide film. That is, the dielectric film 103 is formed of, for example, a silicon oxide film formed by oxidizing the surface of the semiconductor substrate 101.
A conductor film (electrode) 104 is formed on the dielectric film 103. The conductor film 104 is made of, for example, a metal or polysilicon doped with impurities or the like.
Semiconductor capacitor 1000 has a structure excellent in voltage endurance and includes a material excellent in voltage endurance, and therefore it has high voltage endurance. However, it uses a material having resistance to heat and therefore it has high heat resistance.
A semiconductor capacitor has high voltage endurance and high heat resistance as described above. However, a further increase in withstand voltage of the semiconductor capacitor has been required in various devices using the semiconductor capacitor. In such devices, it is advantageous for the device to be driven at as high a voltage as possible since the power loss is reduced. For example, the semiconductor capacitor may be used as a snubber capacitor for a power supply module such as an on-vehicle device, but in an on-vehicle device or the like, it is required to be driven at a voltage as high as possible in order to suppress depletion of a battery as much as possible. With an increases in a voltage of the device, a further increase in withstand voltage has been required for the semiconductor capacitor to be used.
In order to enhance the voltage endurance of the semiconductor capacitor, it is known to increase the thickness of the dielectric film. However, when the thickness of the dielectric film is increased, the intensity of electric field concentration to an end portion of the conductor film (electrode) formed on the dielectric film also increases along with the increase in dielectric film thickness, and therefore the voltage endurance is not significantly improved. For example, even if the thickness of the dielectric film is doubled, the voltage endurance is improved only by, at most, about 1.5 times.
Further, in order to increase the thickness of the dielectric film in the semiconductor capacitor, there is a problem that the time required for forming the dielectric film is prolonged in the manufacturing process of the semiconductor capacitor.